Branhamella catarrhalis belongs to the Neisseriaceae family and a gram stain will reveal a gram negative diplococcus much like those typical for any Neisseria species. It is an aerobic microorganism that is part of the normal human microflora of the nasopharynx. The carrier rate is lower in adults than in children, and nowadays, acute otitis media caused by B. catarrhalis is often found in children. B. catarrhalis is a new pathogen; in 1977, it acquired a new resistance gene capable of inactivating ampicillin. Since then, the percentage of resistant strains isolated in hospitals is increasing steadily and is becoming a problem. Before the 1980's, there was no concern for the correct identification of B. catarrhalis in the microbiology laboratory since it was considered harmless, but since then this microorganism's pathogenic potential has been increasing. Now, many researchers are concerned that clinical laboratories, especially smaller laboratories can not or do not identify B. catarrhalis properly.
Presently, identification of B. catarrhalis in these laboratories is done either by standard biochemical methods, which require at least 48 to 72 hours of incubation time, or by rapid identification tests made for Neisseria and related species. In any case, the clinical sample must first be cultivated and purified since all of these tests require a pure culture as inoculum. Both methods have their advantages and disadvantages. As it was described by Knapp (Microbiological Reviews, vol 1, no. 4, p. 415-431, (1988)), the traditional tests have the advantage that they provide a more detailed characterization of isolates. Unfortunately, they have the major disadvantage that their use may delay the identification of an isolate unnecessarily. In contrast, some rapid tests may not always provide an accurate identification because they give limited information about an isolate.
As far as Branhamella catarrhalis is concerned, identification by standard biochemical methods is time consuming while use of the rapid tests can be inaccurate. Also noticed by Knapp (mentioned above), the species that are the most difficult to distinguish from N. gonorrhoeae by biochemical characteristics are N. cinerea, B. catarrhalis and K. denitrificans.
There are certain biochemical reactions such as the production of acid from glucose and maltose, reduction of nitrate, superoxol production, and colistin susceptibility that can differentiate these species, but some or all of these reactions yield the same results for many Neisseria species and for B. catarrhalis. The only biochemical test that separates B. catarrhalis from the other Neisseria species is the production of an extra-cellular DNase; for which B. catarrhalis tests positive while the others are negative. Although this DNase test can differentiate B. catarrhalis from other Neisseria, it takes at least 72 hours of incubation time before the plates can be read.
In the last 3 or 4 years, rapid identification kits specific for certain genera of bacteria have appeared on the market. Such kits exist for Neisseria and related species. Their major advantage is that most of the common reactions used in standard biochemical identification can all be done at once and in less time. The kits that are presently on the market for Neisseria and related species can be separated into two categories: acid production tests and enzyme substrate tests. A pattern of acid production from a variety of sugars cannot, by itself, provide an identification for B. catarrhalis so enzyme substrate tests have to be used. These tests are based on the observation of the color change of a solution of a chromogenic substrate into which the strain is inoculated. The enzymes tested include: .beta.-galactosidase, .gamma.-glutamylaminopeptidase and hydroxypropylaminopeptidase. Since B. catarrhalis does not produce any of these enzymes, the strain tested is presumptively identified if none of the enzymes are produced by the test isolate (Knapp, J. S., mentioned above). Some kits on the market combine acid production tests and enzyme production tests and these kits provide a better identification of most species. However, these would not be any better for B. catarrhalis since neither of these tests provides a direct identification. Also, only gram-negative, oxidase-positive diplococcal isolates should be inoculated in the tests.
As Knapp stated, the products that incorporate enzyme substrate tests alone must be used according to the limitations of the manufacturer; that is, only strains isolated on selective media should be confirmed in these tests.
Many studies have been done to check the precision of these and other tests for the identification of B. catarrhalis strains. Most of the time, the more popular tests correctly identified 95 to 100% of the Neisseria and related species, but B. catarrhalis identification was always presumptive.
The use of any of these kits or of the standard biochemical methods requires prior purification of the strain from the clinical specimen. Moreover, for the rapid test kits, some preliminary tests such as oxidase production and gram stain have to be performed so that only selected strains are processed with the kits, otherwise, the results might be faulty.
It would be highly desirable if there could be provided a probe specific to Branhamella catarrhalis, which could be used as an identification tool in the clinical microbiology laboratory.
Further, it would also be greatly appreciated if there could be a faster, more reliable, and more direct test for B. catarrhalis available on the market.
Ultimately, it would be a great improvement if there could be a test for B. catarrhalis which requires no purification step.